QPixmapCache: deprecate replace()

The replace() implementation overwrites the passed Key key with a new
version, const_cast'ing away the const from the key passed by
reference-to-const. This is UB if the Key was originally declared
const.

Deprecate the function.

Also inline the const_cast, so compilers can readily detect the UB
even if users don't enable deprecation warnings. Due to the severity
of the issue (UB), immediate deprecation is warranted. There appear to
be no in-tree user of the API outside of tst_qpixmapcache.cpp.

[ChangeLog][Deprecation Notice][QtGui][QPixmapCache] The `replace(key,
pixmap)` function has been deprecated, because passing a `const Key`
to it results in undefined behavior. Use `remove(key, pixmap)`
followed by `key = insert(pixmap)` instead.

Pick-to: 6.6
Change-Id: Ic5060ce3271f2a1b6dc561da8716b452a2355d4c
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>

1 files changed, 17 insertions, 0 deletions

diff --git a/src/gui/image/qpixmapcache.h b/src/gui/image/qpixmapcache.h
index 433890c68f..55aad6503f 100644
--- a/src/gui/image/qpixmapcache.h
+++ b/src/gui/image/qpixmapcache.h
@@ -42,13 +42,30 @@ public:
     static bool find(const Key &key, QPixmap *pixmap);
     static bool insert(const QString &key, const QPixmap &pixmap);
     static Key insert(const QPixmap &pixmap);
+#if QT_DEPRECATED_SINCE(6, 6)
+    QT_DEPRECATED_VERSION_X_6_6("Use remove(key), followed by key = insert(pixmap).")
+    QT_GUI_INLINE_SINCE(6, 6)
     static bool replace(const Key &key, const QPixmap &pixmap);
+#endif
     static void remove(const QString &key);
     static void remove(const Key &key);
     static void clear();
 };
 Q_DECLARE_SHARED(QPixmapCache::Key)
 
+#if QT_DEPRECATED_SINCE(6, 6)
+#if QT_GUI_INLINE_IMPL_SINCE(6, 6)
+bool QPixmapCache::replace(const Key &key, const QPixmap &pixmap)
+{
+    if (!key.isValid())
+        return false;
+    remove(key);
+    const_cast<Key&>(key) = insert(pixmap);
+    return key.isValid();
+}
+#endif // QT_GUI_INLINE_IMPL_SINCE(6, 6)
+#endif // QT_DEPRECATED_SINCE(6, 6)
+
 QT_END_NAMESPACE
 
 #endif // QPIXMAPCACHE_H